1. Field of the invention
This invention relates to a detection reagent which comprises solid fine particles immobilizing an immunologically active substance for a substance to be detected in a test sample and can be used for various immunological detections and assays.
2. Related Background Art
The latex agglutination immunoassay method (LAIA), which assays presence of antigens, etc. by allowing a substance which reacts specifically with the immunologically active substance as mentioned below such as antigen, etc. to react with a dispersion containing solid fine particles such as polystyrene, etc. having an immunologically active substance such as antibody, etc. carried thereon dispersed in a liquid medium such as water, etc. (latex reagent) and observing the agglutination which occurs thereby has been found by J. M. Singer et al, Am. J. Med., 21, 888 (1956), and thereafter various investigations have been made.
The assaying method utilizes LAIA which determines the extent of agglutination by sight. Although quantitative assay may be difficult, the method has the advantage that the assay is simple and the result can be obtained in a short time, therefore it has been practically applied and widely utilized for various detections.
Further, in recent years, it has become possible to make a quantitative assay by LAIA by evaluating the extent of agglutination corresponding to the reaction by way of optical change according to the optical method utilizing an optical instrument, and such quantitative assay is now widely practiced.
The latex reagent to be used for LAIA has solid fine particles having an antibody, immobilized thereon dispersed in a liquid medium as described above.
However, since a dispersion of solid fine particles is an essentially unstable system and, when stored for a long time, agglutination of solid fine particles is liable to occur and, when agglutination has occurred, there will ensue such a problem as lowering in assay sensitivity, etc. Also, when thawed after storage in frozen state, no dispersed state of solid fine particles can be reproduced thereby making it impossible to be utilized for reagent in most cases.
Accordingly, the latex reagent has required special concern regarding storage.
As a method for solving such a problem in storage stability, the method of enhancing storage stability as dry product by drying the latex reagent as the dispersion has been investigated.
For example, Japanese Patent Application Laid-open No. 58-73866 discloses a method in which an agglutinatable immunoreagent such as latex reagent, etc. is placed in a capillary and freeze dried before storage.
However, the latex reagent brought to a dry state has been sufficiently applicable for a qualitative assay, but has proved to be insufficient for application to a quantitative assay by use of an optical method.
More specifically, when the latex reagent is dried according to such method as evaporation, spray drying, freeze drying, vacuum drying, etc., agglutination between solid fine particles will occur, whereby uniform dispersed state of solid fine particles during re-suspension can no longer be obtained and no quantitative analysis with good reproducibility can be done.
As a method for improving the re-dispersibility of the dry latex reagent, for example, Japanese Patent Application Laid-Open No. 52-117420 discloses a method in which a latex reagent added with water-soluble sugars such as lactose, etc. therein is freeze dried under such state to give a dry product.
According to this method, although re-dispersibility of the dry latex reagent is considerably improved by addition of water-soluble sugars, there still remains a problem that no sufficient re-dispersibility demanded in quantitative analysis by use of an optical method can be obtained.
Accordingly, there is the method of increasing the amount added of the additive such as sugars for enhancing re-dispersibility, but use of a large amount of additive exerts deleterious influence such as sensitivity lowering on the immunological reaction, and the increase of the amount added is limited.
Further, there is also the method of obtaining a more uniform re-dispersed state by stirring the dispersion for a long time or at high stirring intensity. However, stirring treatment under strong conditions may result in destruction of the bound state between the immunologically active substance and the solid fine particles or destruction of the immunologically active substance itself. Therefore depending on the bound state between the immunologically active substance and the solid fine particles or the kind of the immunologically active substances, these methods cannot be applied.